There are a number of applications for liquid dispensers which dispense a controlled amount of liquid which contains particles suspended therein. In paint stores, paint pigments are mixed accurately to a formula to create various color tones. These color tones must be able to be accurately reproduced. Therefore, it is necessary to have a dispenser which can dispense controlled amounts of different color pigments easily and quickly. Existing paint pigment dispensers are of two general classes. The first class is a multichannel gear pump. In this device a gear exerts a constant pressure to a pump piston and a valve is opened for a known time. Since pressure is controlled by the gear and the time the valve is open is known, an approximately known amount of pigment is dispensed. The second class of existing systems is a multi-channel device in which a plurality of pistons and valves are provided which are actuated by motors. Since each piston displaces a known volume, a known amount of pigment is dispensed. While this class of system is more precise, it is inordinately expensive to manufacture.
Both of these systems seem to have disadvantages as far as accuracy is concerned. Both are predominately mechanical so as to be both expensive and unreliable. Also, neither are easily amenable to computer control. Therefore, it would be desirable to have a liquid dispenser which can accurately dispense a plurality of different liquids, which is relatively inexpensive, and which is amenable to computer control.
Further, no matter what system one employs, in order to maintain reproducible accuracy, the system should provide mixing means which effectively prevent the settling of particulate matter in the liquid and nozzle means which may be purged and effectively minimizes or eliminates bubbles and dead space, i.e., that is space in which the particlate matter may accumulate and from which it is not readily purged.